Moistureproofing composition and method of making same



Aug. 25, 1936. r. E E E 2,051,944

MOISTUREPROOFiNG COMPOSITION AND METHOD OF MAKING SAME F ilgd July 20, 1933 a Ff ATTORNEY Patented Aug. 25, 1936 UNITED STATES METHOD OF MAKING SAME MOISTUREPROOFING COMPOSITION AND Albert Hershberger, Kenmore, N. Y., assignor, by

mesne assignments, to E. I.

du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware Application July 20, 1933, Serial No. 681,294

4 Claims. (01. 134-17) This invention relates to the manufacture of a glassclear, moistureproof material which is intended primarily for use as a wrapping tissue, though it is capable of other divers uses, such as windows in window envelopes or boxes, in the production of laminated materials, etc. More particularly, the instant invention relates to the composition of matter which is employed as the moistureproofing coating composition and to the method of making the same.

The nature and objects of the invention will become apparent from the appended claims, following description and accompanying drawing forming a part of this specification and wherein:

Figure 1 is a cross-section of a product having a coating thereon formed of a composition constituting the instant invention, and

Figure 2 is a diagrammatic side elevation partly in section of an illustrative apparatus which may be employed in the manufacture of coated material.

The coating composition contemplated by the instant invention comprises a melt which, in its simplest form, is a wax composition containing rubber or an analogous substance, the rubber being present in an amount generally less than 10%, and preferably, when pure rubber is used, approximately 4%-7%, of the total solids. If desired, blending agents, that is, transparentizing, clearing or homogenizing agents, also may be incorporated in the composition. likewise, modifying agents serving to impart certain desirable characteristics to the coating, such as color, hardness, improving the slip thereof, rendering it more favorable to heat-sealing operations, etc., may also be incorporated in the composition.

As the moistureprcofing ingredient, any wax or wax-like or waxy substance capable of moistureproofing may be used. The paraflins, and preferably the high melting point paraiiins, such as those melting over 50 0., such as 55 C. and

preferably approximately. 60 C. or over, are

preferred, since they produce coatings which are characterized by very effective moistureproof qualities, improved slip and freedom from smear when compared to the lower melting point paraffins. Some of these high melting paraflins are commercial products. When, however, the still higher melting point parafiins are desired, they may be obtained, for example, from commercial paraffins by suitable treatment. For instance, the low melting fractions of commercial parafflns may be sweated out or fraction; ted out by means of solvents, or they may be removed by distillation so as to yield a relatively high melting, hard, white, crystalline type of paraflin. Though the hard and high melting point paraflins are definitely preferred, ceresins and some of the hard synthetic or manufactured waxes, for instance various derivatives of the Montan waxes 5 or Montanic acid, may be used as alternatives. The moistureproofing waxes may be used singly or in combination, as may be desired.

As the rubber constituent, pure gum or unvulcanized rubber, such as crepe rubber, is preferred. However, gutta percha, balata, caoutchous, synthetic rubber-like materials, chemical derivatives of rubber, such as thermoprene, hydrogenated thermoprene and other derivatives of thermoprene, hydrogenated rubber, halogenated rubber such as chlorinated rubber and other rubber-like substances, such as the polymers oi. isoprene, butadiene and their homologues, may be used. These rubber or rubber-like sustances may be used singly or in combination with one another, as desired.

The term rubber-like employed in this specifl' cation is intended to cover rubber, chemical derivatives of rubber, derivatives obtained from rubber by physical or chemical treatment and analogous substances, such as those enumerated above.

The rubber or equivalent substance in the composition imparts certain desirable characteristics to the product. It improves the heat-sealing effect of the product and also the flexibility of the coating. It furthermore, tends to improve the adhesion between the coating and the base, and also tends, to a degree, at times, to prevent the crystallization of the waxes. Compositions containing rubber yield a melt of increased viscosity, 5 which viscosity can be regulated by-the amount of rubber used or its degree of degradation. Thus, the melt possesses what might be considered a body which assists in the coating operation in laying down a somewhat thicker and more even coat than would a thin melted body.

Inproducing compositions of the type to which this invention relates, clarity and brilliance in coating, and particularly in the thicker layers, maybe improved by incorporating blending agents in the composition. As illustrative blending agents may be mentioned resins, both natural and synthetic, hydrogenated castor oil, hydrogenated cocoanut oil, hydrogenated cotton-seed oil, stearic acid, anhydrous wool grease, Paraflow," etc., or 50 such materials as diphenyl or B-naphthol when a slight odor is not objectionable.

The resins are characterized by complete solubility in hydrocarbons. Resins, such as ester gum rosin, hydrogenated ester gum, vinyl types of resin which have been so modified as to cause them to be soluble or capable of being dispersed in melted wax, the oil-soluble glyptals, more especially the harder variety, and the chlorinated diphenyl resins, are several illustrative examples of bother resins which may be used.

The blending agents are generally used in minor quantities. They may constitute as much as 20%, although between 5% and 15% of the.

composition is the preferred range. In some cases where the blending agent is oily or a low melting grease, the quantity should be less than 5% of the composition in order to avoid sticky surfaces. The blending agents also improve the gloss and brilliancy of the coating.

The resins, in addition to functioning as blending agents, may also serve to impart additional desired properties to the coating. For example, resins of the film-forming type, such as those of the vinyl type above mentioned, improve the water-resistance of the coating. Again, resins of the film-forming type and/or thermoplastic type, such as the vinyl resins above mentioned, improve the heat-sealing properties of the product.

To achieve other properties in the coatings, a variety of materials or modifying agents which are compatible with the melts may be used. For example, dyes or pigments may be employed to secure color effects or translucency as would be furnished by certain types of pigments. To improve the surface slip of the coating, small quantitles of metallic soaps, such as, for example, less than of zinc or aluminum stearate, may be incorporated in the melt. Small quantities, such as 2% to 10% of the composition, of thermoplastic cellulose derivatives, of which ethyl eellulose, benzyl cellulose, cellulose butyrate, cellulose esters of long chain fatty acids, such as cellulose stearate, cellulose laurate, etc., are examples, may also be employed to increase the heatsealing effect of the coating. For instance, when a cellulose ether of high ethylation, and preferably containing over two ethyl groups, is employed in an amount equal to the rubber constituent, the coating will possess improved heat-sealing properties over the same formula in the absence of ethyl cellulose.

In cases where an increased hardness in the coating is desired, this may be secured by incorporating a wax hardening agent, such as a hard wax, for example, candelilla wax, carnauba wax, the Montan waxes or synthetic derivatives of Montan waxes, bayberry wax, Brazil wax, glycowax B430, etc., either alone or in combination with each other. The quantity of the wax hardening agent may vary from 10% to 60% of the composition.

Optionally, small quantities of softening agents, such as mineral oils, high boiling, odorless, organic liquids, or low melting solids may be used. If desired, materials, such as triethanolamine or triethanolamine soaps, which tend to lower the surface tension between the melt and the base to be coated may be employed.

If desired, vulcanizing agents or anti-oxidants may also be incorporated in the mass. Also, when the quantity of rubber in the composition is such as to impart a tacky surface, this may be overcome by treating the coated material with sulphur chloride, bromide vapor, chlorine gas, ozone, or other chemical agents. After treatment of the finished film with sulphur chloride, etc., the thustreated film is submitted to a process which will remove or destroy the last traces of these vapors.

The compositions may comprise a melt consisting of the ingredients above mentioned or a quasi melt or pseudo melt, that is, the above ingredients together with minor quantities of hydrocarbons or chlorinated hydrocarbons or appropriate solvents. The solvent in such composition is present usually in an amount not exceeding the total quantity of the solid film-forming ingredients and generally to the extent of 25% to 50% of the totalmass. solids and solvents. The use of these solvents does not destroy the character of the mass as a melt. They are used for the purpose of improving the appearance of the final coated sheet and obviating some of the difficulties encountered at times during coating with streaks in the finished product.

Melts containing rubber may be prepared by various procedures. To prepare a melt containing rubber and secure optimum results, the paraflin is milled into the rubber, which may be in sheet form, by calender rolls, preferably made of steel. At the beginning of the operation, the calender rolls are hot and the parafiln is gradually milled into the rubber. As the operation proceeds, the temperature of the rolls is gradually lowered so that by the time approximately equal quantities of the paraffin and rubber have been milled together, the rolls are at room temperature. The rubber and wax mass is then removed from the rolls and blended with the other ingredients of the selectedformula, as hereafter described.

The remainder of the paraflin as well as the other ingredients of the final formula, in their proper proportions, are introduced into a waterjacketed shredder or macerator and heated to a temperature just below the melting point while the knives are in motion. This forms a pasty or semi-pasty mass. To this mass, while it is being agitated by the knives, the proper amount of the rubber-parafiin mass prepared on the calendar rolls is added, either gradually in stages or all at one time. Macerating by the knives is continued at a temperature just suflicient to keep the mass in a pasty condition until complete homogenization of the rubber with the other ingredients takes place, the criterion for which is the absence of lumps when any portion of the mass is taken out and raised to a temperature clearly above its melting point. This operation usually takes several hours. Finally, when the mass has become lump free, it is removed, melted, filtered, and is then ready for use in the coating machine.

In order to more clearly explain the nature of the compositions contemplated by the instant invention, there will hereafter be set forth several specific illustrative examples. It is to be understood that these examples illustrate several embodiments which have given satisfactory results and are not intended to restrict the invention thereto.

Erample III Parts Paraflin (melting point 64 C.) 85 Candelilla wax Rubber 5 Example IV Parts Parafiin (melting point Bil-61 C.) 75 Gum dammar 20 Rubber 5 Example V Parts Paraflln (melting point 60-61 C.) 40 Refined carnauba wax 40 Ester gum"- 15 Rubber 5 I Example VI Parts Paraflin (melting point 64 C.) 60 Refined carnauba wax 20 Gum dammar 15 Rubber 5 Example VII Parts Paramn (melting point 64 C.) 55 Candelilla wax 25 Hydrogenated castor oil 16 Rubber 4 Example VIII Parts Paraffin (melting'point 61-62" C.) 50 Candelilla wax 35 Diphenyl 10 Rubber 5 Example IX Parts Paraffin (melting point 60-6l C.) 45 Refined carnauba wax 45 Rubber 5 High ethylated cellulose 5 Example X Parts Parafiin (melting point 64 C.) 60 Candelilla wax 30 Rubber 5 Zinc stearate 5 The selected composition preferably prepared as above described is applied in the molten state to the base to be coated. After application and before the composition has had time to set, the surplus thereof is removed in any suitable and convenient manner, and simultaneously with, or preferably subsequently to, the surplus-removing operation the composition is subjected to means which function to produce a smooth, glossy and transparent coating. Experimental evidence at the present time shows that in the operation, wherein the coating is smoothed, etc., the wax molecules tend to become oriented in such a manner that their carbon chains stand more or less perpendicular to" the surface of the film. Subsequently, the coating is permitted to set by travel in the air or by projecting thereon a blast of any suitable chilling medium, such as air. After the coating has been set and where the base is of the type which loses moisture during the. process, the coated material may be given a humidifying treating in a' warm moist atmosphere to restore or increase the original flexibility of the base. Finally, the coated film is wound on suitable wind-up device. It is to be noted that the coating, while in the molten state, does not engage with any mechanism other than the surplus-removing device and I the smoothing or wax molecule orientation device until it is in-a set condition.

It is to be noted that in the process described in the immediately preceding paragraph, the wax film or coating is laid down in a glass-clear transparent state. In so far as the prior art is concerned, when a wax coating or film was laid down, it was generally opaque and, at the very best, only translucent.

The product resulting from the aforementioned 'method is diagrammatically illustrated in Figure has given satisfactory'results, the reference numeral 3 designates a supply roll of the base material I which is to be coated and from which it is fed intoa tank 4 containing the molten waxrubber composition and below a freely rotatable roller 5 mounted therein. The tank 4 is provided with any suitable heating mechanism whereby the wax-rubber mix may be melted or, if previously melted, maintained in a melted condition. In the embodiment shown in the drawing, the contents in the tank 4 is heated in any suitable -manner, such as through the medium of an electrically heated oil bath 8. Prior to the immersion of the base I into the molten mass, it may be fed over one or more guide rollers I. From the bath,

the base 'i provided with the molten coatingpasses, preferably, in a vertical direction through to remove the excess composition from the base,

the knives 8, 8 also serve to smooth and impart a glossy surface to the coating:

If desired, a second set of knives I8, Ill may be employed in conjunction with the knives 8, 8. The knives I0, iii are also heated by means of, for

example, electrical heating elements 8, 9, and are provided with edges which have a shorter radius of curvature and therefore are sharper than those of the'knives 8, 8 and which serve to smooth and impart a glossy surface to the coating without removing anycoating from the base. When the two sets of knives are employed, the first set, i. e., 8, 8, merely serves as a surplusremoving element, and the second set, i. e., i8, i8, functions as described.

The knives 8, 8 and I8, iii are preferably made of hard metal. They are highly polished and made as true as possible. In the apparatus illustrated, the knives are overlapped slightly so that the excess composition which is removed depends upon the friction of the sheet upon the knives.

from the time it passes from the first to the secnd set of knives. In other words, the wax mixture on the sheet is still in the molten condition by the time it reaches the second set of electrically heated knives l0, It. If desired, the knives 8, 8 and l0, l0 may be suitably encased. Obviously, .a plurality of sets of knives l0, l0 may be used if desired.

Experimental evidence at this time shows that when the coating is smoothed, etc., either by the knives 8, 8 or knives l0, l0 under the conditions described, the wax molecules tend to become oriented in such a manner that their carbon chains stand more or less perpendicular to the surface of the film.

'After leaving the knives l0, l0, the coated sheet progresses vertically upwards for a distance sufficient to permit the coating to solidify before it engages the guide or roll II. This is important and critical since, if the coating were not solidifiedat the time it engaged the roll I I, it would be smeared or otherwise impaired. From the roll II the coated sheet passes to another guide roll l2 and is finally wound upon a suitable take-up device l3.

When the base I is of the type which loses moisture during the process, the coated material, prior to the winding-up of the coated film, may be subjected to a humidifying treatment in a warm, moist atmosphere. In order to ensure and accelerate the solidification of the coating prior to engaging the roll II, the coated material may be positively cooled, such as by projecting a cooling medium through the nozzles It on to the to improve the transparency and/or gloss of the final product.

Since the amount of wax mixture deposited on the sheet is regulated by the contact of the surplus-removing knife mechanism 8, 8, it is advantageous and desirable to regulate the tension on the sheet as it runs through the machine, so that it will be constant at all times. Otherwise, there will be different amounts of coating deposited on the film depending on the tension variations. The tension may be controlled and regulated by an appropriate means, such as for example, by a suitable braking mechanism .(not shown) cooperating with the supply roll [3.

It is advantageous to use a roll of film which has been cut with a shear cut so that there will be no slivers or loose shreds of the material which will contaminate the coating bath and which later might be carried up, lodging underneath the knives and causing streaks. It is also ad-' visable to pass the material to be coated through one or more dust and dirt removers or wipers l5 which will collect and remove any extraneous materials, including particles of dust or dirt, which might contaminate the bath. The melt should also be protected from falling-dust, dirt and other foreign particles in any suitable manner.

When the method and apparatus described are employed, it frequently happens that small particles of foreign material or dirt lodge beneath the knife and between it and the sheet being coated, thus leaving intermittent streaks in the final product after it is cooled. If there were absolutely no foreign particles in the melt and it could be kept absolutely clean at all times, and if there were absolutely no fiaws or defects in the knives,'there would, of course, be obtained a uniform coating free from streaks or knife scratches. In a practical way, this extreme degree of cleanliness and perfection cannot always be achieved, particularly on a large commercial scale of operation where thousands of feet of film are being run througha bath continuously. It has been found that a considerable portion of 5 these small streaks or scratches can be overcome by theuse of a melt containing minor quantities of solvents, applying the melt by the method hereafter described with no further precautions than those already mentioned. These solvents being present in relatively smallamounts evaporate from the film quite easily and readily after it leaves the last pair of doctor knives and before the film has been wound up. It may or may not be necessary to use special precautions to drive out these solvents depending on the solvents and/or the set of conditions under which the apparatus is operated. These solvents, of course, can be recovered, but usually the quantity is so small that no substantial cost is added to the process by their loss. The use, however, does have a positive effect in producing a film more clearly free from scratches and streaks than is secured without the use thereof.

,By regulating the surplus-removing knives and the tension, the thickness of the coating deposited will be varied within wide limits. When the baseis formed of a sheet or film of regenerated cellulose having a thickness of 0.0009 inch, satisfactory results are secured if the total thickness of the coating on both sides is between 0.00001 and 0.00015 inch depending on the formula of the composition and the process used. Highly satisfactory results are secured when the total thickness of the coating on both sides is 0.00003-0.00005 inch.

Though the invention has been described particularly in connection with sheets or films of regenerated cellulose, it is not restricted thereto. Other membraneous materials which are nonfibrous, non-porous, transparent and have smooth surfaces, such as sheets or films of cellulose derivatives, for example, sheets or films of cellulose nitrate, cellulose acetate, cellulose ethers, or sheetsor films of albuminous materials,

such asgelatin, agar-agar, casein sheets or films .made of a rubber derivative, etc., may be used as the base.

The composition constituting one part of the instant invention produces coatings which are moistureproof, thin, flexible, free from foreign odors, tasteless, non-toxic, heat-scalable for certain purposes where a strong and rugged joint is not required and in the preferred embodiment also glass clear in transparency. They also pos- 5 sess a good gloss and are also characterized by a good surface slip, so that sheets coated therewith will slide easily one over the other. The coatings are also free from an objectionable degree of smearing. They are sufilciently hard so 0 as to withstand objectionable marring or smearing, even when the sheets provided therewith are disposed in stacks or rolls under ordinary weather and temperature conditions. Obviously, the aforementioned properties and characteristics 05 are imparted to the bases coated with the compositions. .By virtue of the fact that the coatings are free from all foreign odors, materials provided with such coatings are entirely suitable for bake goods, which is probably the most critical trade on odors. Likewise, due to the fact that the coatings are tasteless and non-toxic to an extent sufilcient to passany bake goods standard, sheets provided therewith also pass this standard.

By the term moistureproof" as employed in this specification is meant the ability of a sheet or film of regenerated cellulose of a thickness of 0.0009 inch and having a coating on both sides, the total thickness of both coatings not exceeding 0.00015 inch to resist the passage or penetration of moisture or water vapor therethrough to an extent at least 10 times, and preferably 15, 20, 30, 40, 50, 100 or indeed more times, as effective as a sheet or film of regenerated cellulose of the same thickness when tested in accordance with the test set forth in the Journal of Industrial and Engineering Chemistry on page 575, vol. 21, No. 6 (June 1929).

Since it is obvious that various changes and modifications may be made in the above description without departing from the nature or spirit thereof, this invention is not restricted thereto except as set forth in the appended claims.

I claim:

1. A composition-of-matter consisting of a moistureproofing agent; a film-forming substance in an amount less than 10% by weight or the ingredients remaining in the final product and selected from the class which consists of gum rubber, gutta percha. balata, synthetic rubber-like material, chemical derivatives of rubber including Thermoprene, hydrogenated Thermoprene and other derivatives of Thermoprene, hydrogenated rubber, halogenated rubber, rubberlike substances including polymers of isoprene, butadiene and their homologues; and one or more substances which modify the property of the product in an amount not exceeding 60% by weight of the ingredients remaining in the final product and selected from the class which consists of blending agents, substances which increase the heat-sealing effect of the product, substances which increase the hardness of the coating and softening agents; in such relative proportions that the composition will produce from a molten condition a glass-clear transparent, moistureproof, non-tacky coating or film in a thickness said composition producing from a molten condition a glass-clear transparent, moistureproof, non-tacky coating or film in a thickness 0! 0.000005 and 0.000075 inch.

3. A composition-of-matter consisting of Parts by weight Paraffin (melting point 64 C.) 60 Refined carnauba wax 20 Gum dammarl. 15 Rubber 5 said composition producing from a molten condition a glass-clear transparent, moistureproof, non-tacky coating or film in a thickness of 0.000005 and 0.000075 inch.

4. A composition-of-matter consisting of Parts by weight Paraflin (melting point 64 C.) 55 Candelilla wax Hydrogenated castor oil 16 Rubber 4 said composition producing from a molten condition a glassclear transparent, moistureprooi, non-tacky coating or film in a thickness of 0.000005 and 0.000075 inch.

- ALBERT HERSHBERGER. 

